Uni-control heterodyne receiver



May 9, 1933. A. a. MOULTON UNI-CONTROL HBTERODYNE RECEIVER Filed Jan. 27, 1927 iQ a INVENTOR A l NOULTON v BY z a t ORNEY Patented May 9, 1933 UNITED STATES PATENT OFFICE ALBERT B. MOULTON, OF RIVEBHEAD, NEW YORK, ASSIGNOR TO RADIO CORPORATION OF AMERICA, A CORPORATION OF DELAWARE UNI-CONTROL HETEBODYNE RECEIVER Application filed January 87, 1987. Serial No. 163,888.

For ease in tuning receivers having several circuits tuned to the same frequency, unlcontrol systems wherein a single dlal actuates a plurality of similar tuning reactances have been suggested. It has also been suggested to use uni-control where the frequencies are different, as in the case of a heterodyne receiver. When heterodynmg to an audio frequency beat the difference 1n frequencies is relativel slight, and nor arrangements obtain t is difference y means of friction coupling between the reactances and a vernier control, the Vernier being used to relatively shift one of the tunin reactances to obtain the desired beat. Suc an arrangement is disclosed in U. S. Patent No. 1,363,319, to J. L. Hogan, issued December 28, 1920. In this patent the idea of altering a fixed capacity in one of the circuits so as obtain a difference in resonant frequency is also disclosed.

In these prior arrangements when the umcontrol dial is rotated thru its tuning range signals are not audible unless the vernier difference, or the fixed capacity difference, happen to be just right at the correct tunlng point for the particular signal in question.

A fixed capacity difference does not result in a fixed frequency difference, and the variation thereby introduced is aggravated in the case of a superheterodyne receiver, for there the beat frequency is much higher in comparison with the signal frequency, and furthermore, to efficiently use an intermediate frequency amplifier it must be tuned sharply, hence no variation in beat frequency is permissible.

In my invention I recognize that not a constant capacity difference but rather a constant frequency difference must be obtained. Accordingly, an object of my invention is to so vary a plurality of tuning reactances in a plurality of cooperating circuits by means of a single control that there will be a constant frequency difference between the resonant frequencies of the cooperating circuits.

I find that structurally one very convenient way to accomplish this is to use tuning condensers mounted upon a single shaft, or otherwise geared for actuation by a unicontrol means, as heretofore known, but in addition, to appropriately shape the lates of the condensers to obtain the desire constant beat frequency. Accordingly, a further and more specific object of my invention is to so relatively shape the plates of a plurality of tuning condensers connected in circuits coupled for heterodynin that throughout the tuning range of t e condensers the heterodyne frequenc is constant.

The novel features which I elieve to be characteristic of my invention are set forth in particularity in the appended claims, the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawing in which I have indicated diagrammatically one circuit organization whereby my invention may be carried into effect.

The specification is accompanied by a drawing in which:

Figure 1 is a. wiring diagram of a superheterod ne continuous wave receiver in which have embodied my invention;

Figure 2 represents a plate of a tuning condenser;

Figure 3 shows an especially shaped plate for a tuning condenser adapted to cooperate wish the condenser plate shown in Figure 2; an

Figure 4 indicates a graph used in one method of determining the shape of the condenser plate in Figure 3.

Referring to Figure 1 of the drawing the numeral 2 designates a suitable antenna or pick-up circuit to which there is coupled a tuned link circuit 4. The tuned signal frequency circuit 6 is coupled to circuit 4 loosely, and is shielded therefrom by a grounded static screen 8. A local oscillator 10 is also coupled to the signal frequency circuit 6 by means of the coil 12. The tube 14 is given an asymmetric characteristic in any suitable way, exemplified in this instance by the leaky grid condenser 16.

The link circuit 4 and the signal frequency circuit 6 are tuned respectively by the rotary condensers (J and C The local oscillator 10 is tuned by the rotary condenser 0 In this instance I have employed semi-circular plate condensers for C and C and an especially shaped plate condenser for C It is to be understood, however, that the important feature is the relative shape of the plates of con densers C and C rather than their actual shape. For example, it may sometimes be preferable to use condensers having a straight-line tuning characteristic, rather than a straight-line capacity'characteristic. The condensers (1 ,0 and C are all mounted on a single shaft which is rotated by a unicontrol dial.

The intermediate frequency resulting from the heterodyne of the local oscillator 10 and the signal frequency is supplied to an intermediate frequency amplifier 18, and this preferably is very closely tuned to the exact intermediate frequency with which the set is designed to operate. In the case of telephony reception the amplified intermediate frequency energy may be fed directly into any suitable signal detecting and translating means. In the modification disclosed in the drawing, however, which is for continuous wave reception, a second oscillator is employed to beat with the intermediate frequency at an audio frequency. This low frequency oscillator 20 is adjusted to a fixed frequency which differs from the fixed intermediate frequency of the amplifier 18 by the frequency of whatever acoustic note the operator most prefers. The tube 22, like the tube 14, is given an asymmetric characteristic by a leaky grid condenser 24. The input circuit 26 of this tube is fixedly tuned to the intermediate frequency. The audio frequency output of the tube 22 is coupled to an audio frequency amplifier 28, from which some translating device, say the telephone 30, is energized.

It is clear from the description so far that this entire receiver, though apparently complicated, is operated throughout its wave length range by the rotation of but a single control.

The shapes of the plates of the tuning condensers may be computed mathematically, but there is advantage in employing a partially experimental method which I have evolved because it automatically accounts for natural capacitance and inductance in the apparatus as set up for actual operation.

In this method the capacitance of the condenser C for each of some convenient unit of rotation, say five degrees, is first determined. If a semi-circular plate condenser is employed this value is readily computed by simple division. The intermediate frequency amplifier is very closely tuned to the desired intermediate frequency, which may be checked by the use of a wavemeter. A standard measuring condenser is substituted in place of condenser C and for each five degree position of the condenser 0 or the uni-control dial, the condenser C is varied until the beat frequency is correct, as determined by its successful passage through the amplifier 18. The reading of the necessary capacitance C in micromicrofarads for each five degree position of the dial is noted, and each reading is subtracted from the next succeeding reading in order to determine the capacity difference desired between successive five degree positions. A curve may then be plotted, somewhat as in Figure 4, showing the desired capacity difference in micromicrofarads as a function of the angle of r0- tation of the control dial. Since the capacity varies as the area of the plates, and since the area varies as the square of the radius, the ratio of the unknown radius squared, at some angular position a, to the radius squared of the semi-circular plate, will equal the ratio of the capacitance reading on the curve at the angle a, to the constant capacity difference of the semicircular plate condenser.

Expressed as a formula:

M71 TRJT wherein r=radius of the shaped plate condenser at any angle a,

R=radius of the semi-circular plate condenser,

MA=the capacitance reading taken from the curve at the angle a, and

C=the capacitance of the semi-circular plate condenser for each five degrees of rotation.

Any natural coupling in the receiver circuits is automatically compensated for when the standard capacity measurement C is made. If desired, the plates of condenser C may be shifted a suitable number of degrees to take care of the initial capacitance difference between C and C In other cases it may be more desirable to reduce the plate area of C by cutting the necessary amount from its first 5 degree segment.

Although the particular method so far described is for the relative shaping of a condenser for cooperation with a semi-circular plate condenser, my invention is not to be considered as limited to such a modification, for regardless of What shape the condenser C may possess, the measuring condenser C when adjusted to obtain the proper intermediate frequency indicates the correct corresponding capacitance value of C for obtaining constant frequency difference. Itis further to be understood that the condenser C need not be connected in circuit with the oscillator 10 exactly as shown, for other suitable local oscillators such as those having the condenser C connected across the grid circuit, or the plate circuit, or across a grid and plate coil arranged in three point connectlon, may equally well be employed. Un-

der many circumstances thelink circuit 4 may be dispensed with. The antenna, aside from the usual types, may be a wave an tenna or other directional antenna, and for shorter distances a loop or other appropriate pick-up arrangement.

While I have indicated and described one arrangement for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organization shown and described, but that many modifications may be employed without departing from the scope of my invention as set forth in the appended claims.

\Vhat I claim is:

1. A heterodyne receiver comprisin in combination, a resonant circuit tuned y a variable capacity to a signal frequency, a local oscillator circuit tuned by another va' riable capacity to a frequency different from the signal frequency by a desired constant beat frequency, and a single control means for simultaneously varying both tuning capacities, the ratio of said capacities being such that when said control means is varied in equal increments the difference between said capacities is a variable, but said beat frequency is a constant.

2. In combination, a plurality of cooperating circuits tunable to different frequencies of a super-audible difference, a plurality of variable capacities for tuning said circuits, and a single control means for simultaneously varying said tuning capacities, the ratio of said capacities being such that when said control means is varied in equal increments the difference between said capacities is a variable, but the difference frequency between said circuits is a constant.

3. In combination, a plurality of cooperating circuits tunable to different frequencies of a super-audible difference, a plurality of variable condensers for tuning said circuits, and a single control means for simultaneously varying said tuning condensers the capaci ties of said condensers being so proportioned that when said control means is varied in equal increments, the capacity difference betvveen said condensers at each succeeding increment is a variable, but the frequency difference between said circuits is a constai t.

4. A heterodyne receiver including a signal circuit tunable to a signal frequency, an oscillator circuit tunable to a different frequency, each'of said circuits being provided with tuning means including variable condensers, said variable condensers being mounted on a common varying means, the effective capacities of said condensers being so proportioned that when the common means is varied through equal increments the capacity difference of said condensers for each succeeding increment is a variable, but the frequency difference between said circuits is a constant.

5. In a heterodyne receiving system, an antenna. a tuned circuit for received waves, a second tuned circuit for determining the frequency of the. heterodyne wave, a tuned link circuit inductively coupled between the antenna and said receiving circuit, continuously variable condensers included in said tuned circuits, and a control means adapted to adjust said condensers simultaneously, said condensers having non-linear frequency characteristics and being so proportioned and disposed with respect to each other that the resonance frequencies of said tuned link and receiving circuits and said heterodyne circuit differ constantly by a fixed amount while the resonant frequency of one of said tuned circuits is varied over a frequency range of the order of an octave.

6. In combination, in a superheterodyne receiver, an antenna, a tuned link circuit coupled thereto, a frequency changer means having a tuned input circuit inductively coupled to said link circuit, means for electrostatically shielding the antenna from the frequency changer means, a tuned local oscillation circuit coupled to the said tuned input circuit, continuously variable condensers included in each of the said tuned circuits, a single control means for simultaneously adjusting the condensers, said condensers being so proportioned that the resonant frequencies of the tuned link and input circuits differ constantly by a fixed amount from the resonant frequency of the oscillation circuit when the resonant frequency of one of the tuned circuits is varied over a frequency range of the order of an octave.

7. In a superheterodyne receiver, an antenna circuit, a local oscillation circuit comprising an electron discharge tube provided with a tunable input circuit, a variable tuning condenser having a non-linear capacity variation characteristic disposed in said input circuit, a frequency changer circuit comprising an electron discharge tube provided with a tunable input circuit coupled to the input circuit of said oscillator tube, a variable tuning condenser having a linear capacity variation characteristic disposed in said frequency changer input circuit, a tunable oscillation circuit, including a variable tuning condenser having a linear capacity variation characteristic, coupling said antenna circuit and the tunable input circuit of said frequency changer tube, said oscillation circuit being loosely coupled to the frequency changer input circuit, and uni-control means for simultaneously adjusting said variable tuning condensers so that said frequency changer input circuit and said coupling oscillation circuit are tuned to a desired signal frequency and saidoscillator input circuit is tuned to a frequency differing from the desired signal frequencgby a predetprmined constant intermediate equency.

8. In a superheterodyne receiver, an antenna circuit, a local oscillation circuit comprising an electron discharge tube provided with a tunable input circuit, a variable tuning condenser having a non-linear capacity simultaneously adjusting said variable tunvariation characteristic disposed in said input circuit, a frequency changer circuit comprising an electron discharge tube provided with a tunable input circuit coupled to the input circuit of said oscillator tube, a variable tuning condenser having a linear capacity variation characteristic isposed in said frequency changer in ut circuit, a tunable oscillation circuit, inc uding a variable tuning condenser having a linear capacity variation characteristic, cou ling said antenna circuit and the tunable input circuit of said frequency chan er tube, said oscillation circuit being loose y coupled to the frequency changer input circuit, uni-control means for ing condensers so that said frequency changer input circuit and said coupling oscillation circuit are tuned to a desired signal frequency and said oscillator input circuit is tuned to a frequency differing from the desired signal frequency by a predetermined constant intermediate frequency, a second detector circuit including an input circuit tuned to said intermediate frequency and an intermediate frequency amplifier network coupling the output of said frequency changer tube and said second detector input circuit, said network being adapted to pass a band of intermediate frequencies.

9. A superheterodyne receiver including a signal circuit tunable to a desired signal frequency a local oscillator circuit tunable to a di fl'erent frequency, each of said circuits being provided with tuning means including variable condensers, the variable condenser of the signal circuit having a linear capacity variation characteristic and the oscillation circuit variable condenser haying a non-linear capacity variation characteristic, said variable condensers being mounted on a common varying means, the effective capacities of said condensers being so proportioned that when the common means is varied through equal increments, the capacity difference of said condensers for each succeeding increment is a variable, but the frequency difference between said circuits is super-audible and a constant.

a A. B. MOULTON. 

